The present invention relates to a micro beam collimator having an iris like capillary for compressing or concentrating beams. The invention is applicable for the formation of X-ray micro beams or neutron micro beams. Further fields of application are X-ray lithography and the fabrication of miniature mechanical devices.
It is known in the art to use a glass capillary for the formation of X-ray micro beams to provide high resolution in many studies related to material characterization. All prior art developments rely on the principal of total multiple reflections of X-rays from the smooth internal glass capillary surface.
High-resolution X-ray examination on ultra small regions of materials extended the application of numerous laboratory and industrial techniques, such as diffraction, spectroscopy, fluorescence, as well as metal refining, semiconductor and ceramic manufacturing [see prior art references 1,2]. The increasing interest in X-ray microanalysis in many research and commercial fields yielded an intensive demand on methods for formation of X-ray micro beams. Nevertheless the most popular technique still remains the use of glass capillaries with various shapes of longitudinal cross section (usually tapered of parabolic) either single as mono-capillary or bundled as poly-capillary concentrators.
The generation of high intensity X-ray beams in the micrometer size is succeed through the multiple total reflection of X-rays [see prior art references 5,6] inside lead-glass capillary tubes [see prior art references 1–4,7,8]. By directing the source X-rays towards the capillary entrance, the incident beam may compressed as long as the angle of incidence for each reflection remains below the critical value θc which is calculated in the simplified form to θc=(2δ)1/2 and δ=(Ne2λ2Zρ/(2πmc2A), where N=Avogadro's number, e=electron charge, λ=wave length of radiation, Z=atomic number, ρ=material density, m=electron mass, c=velocity of light and A=atomic mass [see prior art references 3, 4].
For lead glass and X-ray photons of 8 KeV, θc does not exceed 3 mrad (0.17°) [see prior art reference 9]. This means that a tapered lead glass capillary about 10 cm long will be limited to an entrance opening of about 20–50 μm if an output beam size of 3–11 μm is required [see prior art references 1,7]; the capillary capture tip must be even smaller for higher photon energies. Hence, only a small fraction of the incident radiation can be condensed, resulting that micro beam experiments usually being conducted at high-energy synchrotron radiation sources with high input X-ray intensities.
A possible way to increase the amount of radiation that can be condensed is to use reflecting materials with higher θc and better properties in the X-ray optics. Ideal materials for such a purpose are the heavyweight metals with high electron densities. Of course, construction of a metallic capillary tube in the style of the classic glass capillary with very smooth inner wall is extremely difficult.
The above mentioned difficulty has been overcome by the micro beam collimator for high resolution XRD investigations according to EP 1 193 492 A1. The known micro beam collimator has a channel for compressing X-ray beams being formed by two opposite, polished, oblong plates made of one of the heavyweight metals or materials having total reflection properties comparable to those of the heavyweight metals. The channel for guiding and compressing the beams has a line- or slit-shaped rectangular cross section. Spacer foils of different thickness can be used depending on the required widths of the generated beam. However, changing the width of the cross section of the channel by replacing the spacer foils is a complicated and time consuming process. Further, the known micro beam collimator does not allow an adjustment of the lengths of the cross section of the channel which is required in some applications.